Method of manufacturing a semiconductor light-emitting device

ABSTRACT

A semiconductor light-emitting device exhibits high reflectance even with less number of pairs of light-reflecting layers, and allows light emitted from the active layer to be effectively extracted outside. This semiconductor light-emitting device is fabricated at good mass productivity by a semiconductor light-emitting device manufacturing method including the step of providing an active layer which generates light having a specified wavelength on a semiconductor substrate. On the semiconductor substrate, are stacked an Al x Ga 1-x As layer and the active layer, in this order. Part of the Al x Ga 1-x As layer with respect to the is changed into an AlO y  layer (where y is a positive real number).

This application is a division of Ser. No. 10/241,728, filed Sep. 12,2002 now U.S. Pat. No. 6,794,688, which is a non-provisional applicationclaiming priority from Japanese Application No. 2001-278104, filed Sep.13, 2001 and Japanese Application No. 2002-234781, filed Aug. 12, 2002.These prior applications are hereby incorporated by reference.

BACKGROUND OF THE INVENTION

The present invention relates to a semiconductor light-emitting devicesuch as light-emitting diodes to be used for display, opticalcommunications and the like, and also to a manufacturing methodtherefor. The invention further relates to an LED lamp and an LEDdisplay, whichever is equipped with such a semiconductor light-emittingdevice.

In recent years, there have been developed high-intensity light-emittingdiodes (LEDs) which emit light of infrared to blue wavelengths. This isbased on the fact that the crystal growth technique fordirect-transition group III-V compound semiconductor materials has beenimproved dramatically so that crystal growth has become implementablefor almost any semiconductor that belongs to the group III-V compoundsemiconductors. LEDs using these direct-transition materials, by virtueof their capability of high-output, high-intensity emission, have cometo be widely used as high-intensity LED lamps such as outdoor displayboards, display-use light sources such as indicator lamps for portableequipment of low power consumption, and light sources for opticaltransmission and optical communications by plastic optical fibers.

As a new high-output, high-intensity LED of this type, there has beenknown an LED using AlGaInP-based material as shown in FIG. 11. This LEDis fabricated by the following process. That is,

On an n-type GaAs substrate 1, are stacked one after another:

-   -   an n-type GaAs buffer layer 2;    -   a distributed Bragg reflector layer (dopant concentration:        5×10¹⁷ cm⁻³) 4 made of a multilayer film in which n-type        (Al_(x)Ga_(1-x))_(0.51)In_(0.49)P (x=0.45) and n-type        Al_(0.51)In_(0.49)P are stacked alternately;    -   an n-type (Al_(x)Ga_(1-x))_(0.51)In_(0.49)P lower cladding layer        (0≦x≦1, e.g. x=1.0; thickness: 1.0 μm; dopant concentration:        5×10¹⁷ cm⁻³) 5;    -   a p-type (Al_(x)Ga_(1-x))_(0.51)In_(0.49)P active layer (0≦x≦1,        e.g. x=0.42; thickness: 0.6 μm; dopant concentration: 1×10¹⁷        cm⁻³) 6; and    -   a p-type (Al_(x)Ga_(1-x))_(0.51)In_(0.49)P upper cladding layer        (0≦x≦1, e.g. x=1.0; thickness: 1.0 μm; dopant concentration:        5×10¹⁷ cm⁻³) 7,    -   and further thereon are formed:    -   a p-type (Al_(x)Ga_(1-x))_(v)In_(1-v)P intermediate layer        (x=0.2; v=0.4; thickness: 0.15 μm; dopant concentration: 1×10¹⁸        cm⁻³) 8;    -   a p-type (Al_(x)Ga_(1-x))_(v)In_(1-v)P current spreading layer        (x=0.05; v=0.05; thickness: 1.5 μm; dopant concentration: 5×10¹⁸        cm⁻³) 10; and    -   an n-type GaP current blocking layer (thickness: 0.3 μm; dopant        concentration: 1×10¹⁸ cm⁻³) 9.

Thereafter, the n-type GaP current blocking layer 9 is subjected toselective etching by normal photolithography process so that a 50 μm to150 μm-dia. portion thereof shown in the figure is left while itssurrounding portions are removed. A p-type (Al_(x)Ga_(1-x))_(v)In_(1-v)Pcurrent spreading layer (x=0.05; v=0.95; thickness: 7 μm; dopantconcentration 5×10¹⁸ cm⁻³) 10 is regrown in such a manner as to coverthe top of the p-type (Al_(x)Ga_(1-x))_(v)In_(1-v)P current spreadinglayer, which has been exposed by removing the n-type GaP currentblocking layer 9, as well as the n-type GaP current blocking layer 9.

Finally, on the p-type current spreading layer 10 is deposited, forexample, a Au—Be film. This film is patterned into a circular form, forexample, so as to be inverse to the light-emitting region, therebyforming a p-type electrode 12. Meanwhile, on the lower surface of theGaAs substrate 1 is formed, for example, an n-type electrode 11 made ofa Au—Zn film by deposition.

It is noted here that, for simplicity' sake, the ratio x of Al to Ga,the ratio v of totaled Al and Ga to the other group III elements, or thelike will be omitted as appropriate in the following description.

With respect to the p-type AlGaInP current spreading layer 10, the Alcomposition “x” and the In composition (1-v) are set low, as alreadydescribed, so that the current spreading layer becomes transparent tothe emission wavelength range 550 nm-670 nm of this AlGaInP-based LED,low in resistivity, and makes ohmic contact with the p-side electrode(i.e., x=0.05, v=0.95). In the AlGaInP-based LED, normally, Si is usedas the n-type dopant, and Zn is used as the p-type dopant. Also, theconductive type of the active layer is normally the p type.

As the substrate for (Al_(x)Ga_(1-x))_(v)In_(1-v)P-based LEDs, normally,a GaAs substrate is used so as to obtain lattice matching with materialsof individual layers. However, the GaAs substrate has a band gap of 1.42eV, lower than those of (Al_(x)Ga_(1-x))_(v)In_(1-v)P-basedsemiconductors, so that the GaAs substrate would absorb light emissionof 550 nm to 670 nm, which is a wavelength range of(Al_(x)Ga_(1-x))_(v)In_(1-v)P-based semiconductors. Therefore, out oflight emitted from the active layer, the light emitted toward thesubstrate side would be absorbed within the chip, and could not beextracted outside. Accordingly, for (Al_(x)Ga_(1-x))_(v)In_(1-v)P-basedLEDs, with a view to fabricating a high-efficiency, high-intensity LED,it is important to provide a DBR (distributed Bragg reflector) layer 4in which low-refractive-index layer and high-refractive-index layer arecombined one after another between the GaAs substrate 1 and the activelayer 6 as shown in FIG. 11 so as to obtain an enhanced reflectancethrough multiple reflection. In this example of FIG. 11,(Al_(0.65)Ga_(0.35))_(0.51)In_(0.49)P (refractive index: 3.51) that doesnot absorb the emission wavelength 570 nm of the active layer isselected as the high-refractive-index material, and Al_(0.51)In_(0.49)P(refractive index: 3.35) is selected as the low-refractive-indexmaterial, while optical film thicknesses of the individuallow-refractive-index layer and high-refractive-index layer are set toλ/4 relative to an emission wavelength of λ. These materials are stackedalternately to an extent of 10 pairs so as to be enhanced inreflectance, by which the total photoreflection-layer reflectance is setto about 50%. In a case where such an AlGaInP-based light-reflectinglayer is provided, reflectance characteristics against the number ofpairs are shown in FIG. 13A. The expression “AlInP/Q(0.4)” in the figureindicates a characteristic with the use of a pair of(Al_(0.65)Ga_(0.35))_(0.51)In_(0.49)P and Al_(0.51)In_(0.49)P.Similarly, the expression “AlInP/Q(0.5)” indicates a characteristic withthe use of a pair of (Al_(0.55)Ga_(0.45))_(0.51)In_(0.49)P andAl_(0.51)In_(0.49)P With this light-reflecting layer adopted, the chipluminous intensity can be improved from 20 mcd to 35 mcd, compared withthe case where no light-reflecting layer is provided.

As is well known, if the layer thickness of crystals is “d” and therefractive index is “n,” then the optical film thickness is given by“nd.”

As shown in FIG. 12, in (Al_(x)Ga_(1-x))_(v)In_(1-v)P-based LEDs is useda light-reflecting layer 14 which is formed by stacking a pair ofAl_(x)Ga_(1-x)As and AlAs and which has lattice matching with the GaAssubstrate. In a case where such an AlGaAs-based light-reflecting layer14 is provided, reflectance characteristics against the number of pairsare shown in FIG. 13B. In the figure, a broken line expressed as“Al_(0.60)” shows a characteristic with the provision of alight-reflecting layer which is formed by selecting Al_(0.65)Ga_(0.35)As(refractive index: 3.66), which does not absorb the emission wavelength570 nm of the active layer, as the high-refractive-index material andselecting AlAs (refractive index: 3.10) as the low-refractive-indexmaterial, and then stacking alternately these materials as a pair.Similarly, a broken line expressed as “Al_(0.70)” in the figure shows acharacteristic with the use of a pair of Al_(0.70)Ga_(0.30)As and AlAs,and a solid line expressed as “Al_(0.75)” in the figure shows acharacteristic with the use of a pair of Al_(0.65)Ga_(0.35)As and AlAs.As a result of this, in the case where Al_(0.65)Ga_(0.35)As (refractiveindex: 3.66) is selected as the high-refractive-index material and AlAs(refractive index: 3.10) is selected as the low-refractive-indexmaterial, it becomes possible to provide a larger difference inrefractive index than in the case shown in FIG. 13A, where the totalreflectance of the light-reflecting layer can be made to be about 60%.With this light-reflecting layer adopted, the chip luminous intensitycan be improved from 20 mcd to 40 mcd, compared with the case where nolight-reflecting layer is provided.

In this connection, as can be understood from FIGS. 13A and 13B, inorder to obtain a high reflectance of 90% or more, which allows theluminous intensity to be improved double or more, the number ofsemiconductor layer pairs constituting the light-reflecting layer 4, 14needs to be 30 or more. This is due to very small differences inrefractive index, which are 0.18 in the case of(Al_(x)Ga_(1-x))_(0.51)In_(0.49)P(x=0.45)/Al_(0.51)In_(0.49)P and 0.32or so in the case of AlAs/Al_(x)Ga_(1-x)As.

However, providing a pair number of 30 or more would cause the growthtime to be prolonged, which would lead to lower mass-productivity. Also,small differences in refractive index would cause the half-value widthof the reflection spectrum to be narrowed, where only a slight change inlayer thickness of the light-reflecting layer would cause the reflectionspectrum to be largely shifted, making it difficult to obtain a matchingbetween emission wavelength and light-reflecting layer, which would leadto lower reproducibility and so lower mass-productivity. Further, withthe number of pairs increased, the light-reflecting layer alone wouldtake a layer thickness as thick as 3 μm or more, where the substrateafter epitaxial growth would be liable to warp or deformation, making itdifficult to subject the substrate to subsequent processes.

These circumstances are the same also with semiconductor light-emittingdevices using other various materials without being limited to theAlGaInP-based materials.

SUMMARY OF THE INVENTION

Accordingly, an object of the present invention is to provide asemiconductor light-emitting device capable of effectively extractinglight emitted from the active layer to the external.

Another object of the present invention is to provide a semiconductorlight-emitting device manufacturing method capable of fabricating suchsemiconductor light-emitting devices with high mass-productivity.

Still further object of the present invention is to provide an LED lampand LED display equipped with such semiconductor light-emitting devices.

In order to achieve the above object, the semiconductor light-emittingdevice of the present invention has the following constitution. That is,the semiconductor light-emitting device of the present invention isformed by stacking, on a semiconductor substrate, a plurality of layersincluding an active layer made of a semiconductor which generates lightof a specified wavelength. Furthermore, the semiconductor light-emittingdevice comprises a first light-reflecting layer provided between thesemiconductor substrate and the active layer and having a mainreflecting part including a dielectric containing Al or space and a subreflecting part made of a semiconductor layer containing Al.

In the semiconductor light-emitting device of this invention, betweenthe semiconductor substrate and the active layer is a firstlight-reflecting layer having a main reflecting part including adielectric containing Al or space and a sub reflecting part made of asemiconductor layer containing Al. The main reflecting part of thisfirst light-reflecting layer, by virtue of its including an dielectriccontaining Al or space, becomes lower in refractive index “n” than thesub reflecting part formed of a semiconductor layer containing Al.Accordingly, light emitted by the active layer is reflected at a highreflectance by the main reflecting part of the first light-reflectinglayer. If the main reflecting part of the first light-reflecting layeris disposed at a necessary region, e.g., at a region where the electrodeis absent on the active layer, then the light emitted by the activelayer is reflected by the main reflecting part of the firstlight-reflecting layer so as to go outside without being interrupted bythe electrode. Therefore, light emitted from the active layer can beextracted outside effectively.

In one embodiment, the semiconductor light-emitting device furthercomprises a second light-reflecting layer provided between the firstlight-reflecting layer and the active layer and formed by stacking aplurality of pairs of a low-refractive-index material layer and ahigh-refractive-index material layer.

In the semiconductor light-emitting device of this one embodiment,between the first light-reflecting layer and the active layer is asecond light-reflecting layer formed by stacking a plurality of pairs ofa low-refractive-index material layer and a high-refractive-indexmaterial layer. Therefore, light emitted from the active layer can beextracted outside further effectively. Also, by virtue of a lowrefractive index “n” of the main reflecting part of the firstlight-reflecting layer, a high reflectance can be obtained even with asmall number of pairs of the second light-reflecting layer.

Desirably, the second light-reflecting layer is a distributed Braggreflector (DBR).

In one embodiment of the semiconductor light-emitting device, thesemiconductor substrate is of a first conductive type, and asecond-conductive-type current spreading layer is provided on the activelayer. The semiconductor light-emitting device further comprises afirst-conductive-type current blocking layer provided at a specifiedregion inside the current spreading layer, and an electrode layerprovided on an top surface of the current spreading layer and at aregion corresponding to the current blocking layer. Furthermore, the subreflecting part of the first light-reflecting layer is disposed at aregion corresponding to the current blocking layer, and the mainreflecting part of the first light-reflecting layer is disposed at aregion corresponding to surroundings of the current blocking layer.

In the semiconductor light-emitting device of this one embodiment,electric current injected from the electrode layer into the currentspreading layer is interrupted by the current blocking layer provided ata specified region inside the current spreading layer, and thus flows inmore part to the surrounding region of the current blocking layer. As aresult, light emission occurs more in a portion of the active layercorresponding to the surroundings of the current blocking layer. Sincethe main reflecting part of the first light-reflecting layer is disposedat a region corresponding to the surroundings of the current blockinglayer, light emitted at the portion of the active layer corresponding tothe surroundings of the current blocking layer is reflected by the mainreflecting part of the first light-reflecting layer so as to go outsidewithout being interrupted by the electrode. Therefore, light emittedfrom the active layer can be extracted outside effectively.

In one embodiment of the semiconductor light-emitting device, the subreflecting part of the first light-reflecting layer is formed of any onekind of semiconductor selected from among Al_(x)Ga_(1-x)As,(Al_(x)Ga_(1-x))_(v)In_(1-v)P, (Al_(x)Ga_(1-x))_(v)In_(1-v)N,(Al_(x)Ga_(1-x))_(v)In_(1-v)As, and (Al_(x)Ga_(1-x))_(v)In_(1-v)Sb(where 0<x≦1 and 0<v<1), and the main reflecting part of the firstlight-reflecting layer is formed of AlO_(y) (where y is a positive realnumber) or space.

Herein, aluminium oxide is expressed uniformly as AlO_(y), and AlO_(y)is synonymous with Al_(x)O_(y) (where x and y are positive realnumbers).

In addition, it is assumed that suffixes “x,” “v,” “y” and the likerepresenting compositions can take independent values between and amongdifferent compounds.

In one embodiment of the semiconductor light-emitting device, the subreflecting part of the first light-reflecting layer is formed of any onekind of multilayer film selected from among a multilayer film in whichAl_(x)Ga_(1-x)As layer and Al_(z)Ga_(1-z)As layer are alternatelystacked, a multilayer film in which (Al_(x)Ga_(1-x))_(v)In_(1-v)P layerand (Al_(z)Ga_(1-z))_(v)In_(1-v)P layer, alternately stacked, amultilayer film in which (Al_(x)Ga_(1-x))_(v)In_(1-v)N layer and(Al_(z)Ga_(1-z))_(v)In_(1-v)N layer alternately stacked, a multilayerfilm in which (Al_(x)Ga_(1-x))_(v)In_(1-v)As layer and(Al_(z)Ga_(1-z))_(v)In_(1-v)As layer are alternately stacked, and amultilayer film in which (Al_(x)Ga_(1-x))_(v)In_(1-v)Sb layer and(Al_(z)Ga_(1-z))_(v)In_(1-v)Sb layer are alternately stacked (where0<x<z≦1 and 0<v<1), and the main reflecting part of the firstlight-reflecting layer is formed of a multilayer film in which any onekind of semiconductor selected from among Al_(x)Ga_(1-x)As,(Al_(x)Ga_(1-x))_(v)In_(1-v)P, (Al_(x)Ga_(1-x))_(v)In_(1-v)N,(Al_(x)Ga_(1-x))_(v)In_(1-v)As, and (Al_(x)Ga_(1-x))_(v)In_(1-v)Sb(where 0<x≦1 and 0<v<1) in correspondence to the multilayer film formingthe sub reflecting part, and AlO_(y) layer (where y is a positive realnumber) or a space layer, are alternately stacked.

As described in conjunction with the prior art, in order to enhance thelight extraction efficiency by obtaining a high reflectance with thelight-reflecting layer so that higher brightness and higher output canbe achieved, given that the light-reflecting layer is a single layer,there is a need for obtaining a larger difference in refractive indexbetween two layers that define the reflecting surface of thelight-reflecting layer. Also, when the light-reflecting layer is formedof a multilayer film, it is necessary to obtain a larger difference inrefractive index between a pair of semiconductor films constituting thelight-reflecting layer. However, for example, in the case of(Al_(x)Ga_(1-x))_(v)In_(1-v)P-based LEDs, materials that are free fromlight absorption and that come into lattice matching with the activelayer are limited to (Al_(x)Ga_(1-x))_(v)In_(1-v)P-based materials orAl_(x)Ga_(1-x)As-based materials, which are compound semiconductormaterials in either case, where the refractive index can be changed onlywithin a range of 2.9 to 3.5 or so at most.

On the other hand, a principle diagram of the reflection layer of thepresent invention is shown in FIG. 1. This is a structure in which on asemiconductor substrate “a” are deposited, in this order, an AlO_(y)oxide layer “b,” which is formed by oxidizing AlAs, an Al_(x)Ga_(1-x)Aslayer, a light-reflecting layer “c,” which is formed by alternatelystacking a high-refractive-index semiconductor material and alow-refractive-index semiconductor material, and an active layer “d.” Incontrast to this, the prior art includes no AlO_(y) oxide layer “b.”With the shown arrangement, there can be provided a refractive indexdifference as large as 0.6 to 1.4 or so between the light-reflectinglayer “c” and the AlO_(y) layer “b.” Therefore, the reflectance at theinterface between the light-reflecting layer “c” and the AlO_(y) layer“b” becomes larger, so that a larger reflectance can be obtained ascompared with normal light-reflecting layers. For example, as shown inFIG. 2, according to the present invention, a higher reflectance can beobtained as compared with the case where the AlO_(y) layer is notprovided (prior art), and yet the half-value width of the reflectionspectrum can be increased (the wavelength range with high reflectance iswidened).

Meanwhile, a principle diagram of another reflection layer according tothe present invention is shown in FIG. 3. This is a structure in whichon a semiconductor substrate “a” are deposited, in this order, alight-reflecting layer “f,” which is formed by alternately stacking AlAslayer and Al_(x)Ga_(1-x)As layer and further changing the AlAs layerinto an AlO_(y) layer (where y is a positive real number) “b,” and anactive layer “d.” As compared with the conventional light-reflectinglayer in which AlAs layer and Al_(x)Ga_(1-x)As layer are alternatelystacked as they are, in contrast to this, there can be provided arefractive index difference as large as 0.6 to 1.4 or so between theAlO_(y) layer and the Al_(x)Ga_(1-x)As layer. As a result, reflectioncharacteristic of the light-reflecting layer “f” shows a highreflectance of 99% at maximum as shown in FIG. 4, with its wavelengthrange also widened. Further, since the reflectance abruptly decreasesfor light of wavelengths falling outside the necessary wavelength range,the semiconductor light-emitting device is enhanced in color purity asanother advantage. As in the case of FIG. 1, even with variations orfluctuations in layer thickness, reflectance and reflection spectrum areless liable to variations, hence a high mass productivity.

Al is strong in bond with oxygen, so highly oxidation-prone, and only byleaving it in the air, Al oxide is formed. However, the Al oxide filmformed only by natural oxidation as shown above is poor incharacteristics, exemplified by large numbers of voids in the film.Accordingly, for example, leaving an Al_(x)Ga_(1-x)As layer (inparticular, one having an Al composition of nearly 1) in a water vaporatmosphere at a temperature of 300° C. to 400° C. allows Al to beoxidized by high-temperature water vapor, so that stabler AlO_(y) layercan be formed (e.g., Specification of U.S. Pat. No. 5,517,039, orKenichi Iga et al., “Fundamentals and Applications of Plane EmissionLaser,” Kyoritsu Shuppan K. K., June 1999, pp. 105-113.) This AlO_(y)layer, because of being an oxide (dielectric), is much lower inrefractive index “n” than semiconductor materials, taking a value ofn=2.5 to 1.9. Accordingly, by changing the Al_(x)Ga_(1-x)As layer intoan AlO_(y) layer so that the refractive index is lowered, thereflectance for the light emitted by the active layer can be enhanced.Thus, a high reflectance can be obtained even with a small number ofpairs in the light-reflecting layer, and the light emitted from theactive layer can be extracted outside effectively.

Also, the AlO_(y) layer, because of being an oxide (dielectric), islarge in band gap, and transparent to blue to red visible light regions.Therefore, according to the present invention, a high-qualitylight-reflecting layer which is very small in wavelength dependence andwhich is close to 100% in reflectance can be formed. As a result ofthis, it is no longer necessary to laboriously select an Al compositionwhich is free from absorption to emission wavelength, as would beinvolved in the light-reflecting layer made of semiconductor materialsof the prior art.

According to the present invention, a high reflectance can be obtainedas compared with the case where the AlO_(y) layer is not provided (priorart), and yet the half-value width of the reflection spectrum can beincreased. As a result, even with variations or fluctuations in layerthickness of the light-reflecting layer, reflectance and reflectionspectrum are less liable to variations, hence a high mass productivity.

Since the low-refractive-index Al rich layer “f₂” constituting thelight-reflecting layer becomes an AlO_(y) layer having an even lowerrefractive index, the reflectance for the light emitted by the activelayer can be enhanced. Thus, a high reflectance can be obtained evenwith a small number of pairs of the light-reflecting layer, and thelight emitted from the active layer can be extracted outsideeffectively. For example, as shown in FIG. 4, according to the presentinvention, a higher reflectance can be obtained as compared with thecase where the AlO_(y) layer is not changed into an AlO_(y) layer (priorart), and yet the half-value width of the reflection spectrum can beincreased. As a result, even with variations or fluctuations in layerthickness of the light-reflecting layer, reflectance and reflectionspectrum are less liable to variations, hence a high mass productivity.

FIG. 5 shows a pair-number dependence of the reflectance of thelight-reflecting layer according to the present invention, in comparisonwith prior arts. In the figure, a solid line α connecting marks “•” toone another shows a characteristic with the use of a pair of alow-refractive-index AlO_(y) layer and a high-refractive-indexAl_(0.60)Ga_(0.40)As layer according to the present invention, while theother lines β1, β2, β3, β4 and β5 show characteristics with the use ofknown pairs. More specifically, β1 shows a characteristic with the useof a pair of Al_(0.75)Ga_(0.25)As layer and AlAs layer, β2 shows acharacteristic with the use of a pair of Al_(0.70)Ga_(0.30)As layer andAlAs layer, β3 shows a characteristic with the use of a pair ofAl_(0.60)Ga_(0.40)As layer and AlAs layer, β4 shows a characteristicwith the use of a pair of (Al_(0.40)Ga_(0.60))_(0.51)In_(0.49)P layerand Al_(0.51)In_(0.49)P layer, and β5 shows a characteristic with theuse of a pair of (Al_(0.50)Ga_(0.50))_(0.51)In_(0.49)P layer andAl_(0.51)In_(0.49)P layer. As can be understood from the figure,according to the present invention, the light-reflecting layer, byvirtue of its large refractive index difference, can achieve areflectance of almost 100% even with a few pairs of the light-reflectinglayer. Thus, the growth time can be reduced and a high mass productivitycan be obtained.

The method for manufacturing a semiconductor light-emitting device ofthe present invention has the following constitution. That is, themethod for manufacturing a semiconductor light-emitting device of thepresent invention is one of stacking, on a semiconductor substrate, aplurality of layers including an active layer made of a semiconductorwhich generates light of a specified wavelength. Furthermore, the methodcomprising the steps of:

-   -   providing, between the semiconductor substrate and the active        layer, an Al rich layer higher in Al ratio than any other layer        among the plurality of layers;    -   dividing into chips a wafer in which the plurality of layers are        stacked, thereby making a side face of the Al rich layer        exposed; and    -   oxidizing Al contained in the Al rich layer from the exposed        side face, thereby making a peripheral portion of the Al rich        layer changed into an AlO_(y) layer.

In the semiconductor light-emitting device manufacturing method of thisinvention, peripheral portion of the Al rich layer is changed into anAlO_(y) layer (dielectric) so that the refractive index is lowered, bywhich the reflectance for the light emitted by the active layer can beenhanced. Thus, the light emitted from the active layer can be extractedoutside effectively.

In one embodiment of the method for manufacturing a semiconductorlight-emitting device, the step of oxidizing Al contained in the Al richlayer is carried out by leaving in a water vapor the chips in which theside face of the Al rich layer is exposed.

In one embodiment of the method for manufacturing a semiconductorlight-emitting device, the water vapor is introduced to the side face ofthe Al rich layer by an inert gas that has been passed through boilingwater.

In one embodiment of the method for manufacturing a semiconductorlight-emitting device, the step of oxidizing Al contained in the Al richlayer is carried out in an atmosphere having a temperature of 300° C. to400° C.

In one embodiment, the method for manufacturing a semiconductorlight-emitting device further comprises the step of removing, byetching, the AlO_(y) layer formed at the peripheral portion of the Alrich layer.

In the semiconductor light-emitting device manufacturing method of thisone embodiment, since the space region formed by the removal of theAlO_(y) layer has a refractive index of 1, a nearly total reflectionstate can be obtained at the chip peripheral portion of the rear side ofthe active layer. Thus, the light emitted from the active layer can beextracted outside effectively.

Also, according to the present invention, there is provided an LED lampwhich comprises the semiconductor light-emitting device as definedabove.

In one embodiment of the LED lamp, as said semiconductor light-emittingdevice, a plurality of semiconductor light-emitting devices havingdifferent wavelengths from each other are integrally provided, and thesemiconductor light-emitting devices are connected in the manner thatthey can be applied with electric current independently from each other.

Also, according to the present invention, there is provided an LEDdisplay in which the LED lamp as defined above is arrayed in a matrix.

In one embodiment, there is provided a method for manufacturing asemiconductor light-emitting device, including the step of forming anelectrode for electrical conduction at a region above the active layercorresponding to a remaining portion of the Al rich layer that is notchanged into the AlO_(y) layer.

In the semiconductor light-emitting device manufacturing method of thisone embodiment, an electrode is formed at a region above the activelayer corresponding to a remaining portion of the Al rich layer that isnot changed into the AlO_(y) layer. Therefore, out of the Al rich layer,the region corresponding to the portion that has been changed into theAlO_(y) layer can be prevented from being occupied by the electrode.Thus, the light generated by the active layer and reflected by theAlO_(y) layer can be extracted outside effectively without beinginterrupted by the electrode.

In one embodiment, there is provided a method for manufacturing asemiconductor light-emitting device, including the step of forming acurrent blocking layer for blocking electric current at a regioncorresponding to a remaining portion of the Al rich layer that is notchanged into the AlO_(y) layer.

In the semiconductor light-emitting device manufacturing method of thisone embodiment, a current blocking layer for blocking electric currentis formed at a region corresponding to its remaining portion that is notchanged into the AlO_(y) layer. Therefore, a larger amount of electriccurrent flows through the region corresponding to the AlO_(y) layer, ascompared with the case where the current blocking layer is not formed.Thus, the light generated by the active layer and reflected by theAlO_(y) layer can be extracted outside effectively.

In one embodiment, there is provided a method for manufacturing asemiconductor light-emitting device, wherein the light-reflecting layeris formed by alternately stacking a layer containing Al and having aspecified Al composition and an AlO_(y) layer, and thickness of onelayer which is among the layers forming the light-reflecting layer andwhich is adjacent to the layer containing Al and changed into theAlO_(y) layer is set to a quarter of the wavelength.

In one embodiment, there is provided a method for manufacturing asemiconductor light-emitting device, further including the step of,after dividing the layers into chips, making the Al rich layer changedinto the AlO_(y) layer from its exposed end face, where a remainingportion of the Al rich layer that is not changed into the AlO_(y) layeris made coincident in configuration with the electrode above the activelayer.

In the semiconductor light-emitting device manufacturing method of thisone embodiment, it is no longer necessary to laboriously select an Alcomposition which is free from absorption to emission wavelength, aswould be involved in the light-reflecting layer made of semiconductormaterials of the prior art.

In another aspect of the semiconductor light-emitting device of thisinvention, there is provided a semiconductor light-emitting devicehaving on a semiconductor substrate a light-emitting layer whichgenerates light of a specified wavelength, the semiconductorlight-emitting device further including, between the semiconductorsubstrate and the light-emitting layer, a semiconductor layer which hasa refractive index varying with respect to a layer direction so as toreflect light emitted by the light-emitting layer.

It is noted here that the terms, “layer direction,” refer to a directionextending along the layer, i.e., a direction (planar direction) alongwhich the layer spreads.

In the semiconductor light-emitting device of this invention, betweenthe semiconductor substrate and the light-emitting layer, is provided asemiconductor layer which has a refractive index varying with respect toa layer direction so as to reflect light emitted by the light-emittinglayer. The refractive index of this semiconductor layer is so set as tobe lower in a necessary region, for example, a region where theelectrode is absent above the light-emitting layer, by which thereflectance for the light emitted by the light-emitting layer can beenhanced. Thus, a high reflectance can be obtained even with a smallnumber of pairs in the light-reflecting layer, and the light emittedfrom the light-emitting layer can be extracted outside effectively.

As already described, in order to enhance the light extractionefficiency by obtaining a high reflectance with the light-reflectinglayer so that higher brightness and higher output can be achieved, thereis a need for obtaining a larger difference in refractive index betweena pair of semiconductor films constituting the light-reflecting layer.However, for example, in the case of (Al_(x)Ga_(1-x))_(v)In_(1-v)P-basedLEDs, materials that are free from light absorption and that come intolattice matching with the light-emitting layer are limited to(Al_(x)Ga_(1-x))_(v)In_(1-v)P-based materials or Al_(x)Ga_(1-x)As-basedmaterials, which are compound semiconductor materials in either case,where the refractive index can be changed only within a range of 2.9 to3.5 or so at most.

Accordingly, as a method for manufacturing a semiconductorlight-emitting device in the present invention, there is provided asemiconductor light-emitting device manufacturing method including astep of providing on a semiconductor substrate a light-emitting layerwhich generates light of a specified wavelength, the method furthercomprising the steps of depositing an Al_(x)Ga_(1-x)As layer and thelight-emitting layer on the semiconductor substrate in this order, andmaking part of the Al_(x)Ga_(1-x)As layer in the layer direction changedinto an AlO_(y) layer (where y is a positive real number).

Al in the Al_(x)Ga_(1-x)As layer is strong in bond with oxygen, sohighly oxidation-prone, and when it is left in the air, Al oxide isformed. Accordingly, oxidizing an Al_(x)Ga_(1-x)As layer (in particular,one having an Al composition “x” of nearly 1) in a water vapor at atemperature of 300° C. to 400° C. allows a stable AlO_(y) layer to beformed. This AlO_(y) layer, because of being an oxide containing Al, ismuch lower in refractive index “n” than semiconductor materials, takinga value of n=2.5 to 1.9. Accordingly, by changing the Al_(x)Ga_(1-x)Aslayer into an AlO_(y) layer so that the refractive index is lowered, thereflectance for the light emitted by the light-emitting layer can beenhanced. Thus, a high reflectance can be obtained even with a smallnumber of pairs in the light-reflecting layer, and the light emittedfrom the light-emitting layer can be extracted outside effectively.

Also, the AlO_(y) layer, because of being an oxide, is large in bandgap, and transparent to visible light regions, particularly a region of560 nm to 650 nm, which is the emission region of(Al_(x)Ga_(1-x))_(v)In_(1-v)P-based materials. Therefore, according tothe present invention, a high-quality light-reflecting layer which isvery small in wavelength dependence and which is close to 100% inreflectance can be formed. As a result of this, it is no longernecessary to laboriously select an Al composition which is free fromabsorption to emission wavelength, as would be involved in thelight-reflecting layer made of semiconductor materials of the prior art.

In a method for manufacturing a semiconductor light-emitting device inone embodiment, as illustrated in FIG. 1, an Al_(x)Ga_(1-x)As layer, alight-reflecting layer “c” in which a high-refractive-index material anda low-refractive-index material are alternately stacked, and alight-emitting layer “d” are deposited in this order on a semiconductorsubstrate “a,” and then part of the Al_(x)Ga_(1-x)As layer in the layerdirection is changed into an AlO_(y) layer “b” (FIG. 1, however, showsonly a region that has been changed into the AlO_(y) layer). With suchan arrangement, a refractive index difference as large as 0.6 to 1.4 orso can be provided between the light-reflecting layer “c” and theAlO_(y) layer “b.” Therefore, the reflectance at the interface betweenthe light-reflecting layer “c” and the AlO_(y) layer “b” becomes larger,so that a larger reflectance can be obtained as compared with normallight-reflecting layers. For example, as shown in FIG. 2, according tothe present invention, a higher reflectance can be obtained as comparedwith the case where the AlO_(y) layer is not provided (prior art), andyet the half-value width of the reflection spectrum can be increased. Asa result, even with variations or fluctuations in layer thickness of thelight-reflecting layer, reflectance and reflection spectrum are lessliable to variations, hence a high mass productivity.

In a method for manufacturing a semiconductor light-emitting device inone embodiment, as illustrated in FIG. 3, a light-reflecting layer “f”in which a high-refractive-index semiconductor material “f₁” and alow-refractive-index Al_(x)Ga_(1-x)As layer “f₂” (where 0<x≦1) arealternately stacked, and a light-emitting layer “d” are deposited inthis order on a semiconductor substrate “a,” and then part of theAl_(x)Ga_(1-x)As layer “f₂” in the layer direction is changed into anAlO_(y) layer (FIG. 3, however, shows only a region (dotted) that hasbeen changed into the AlO_(y) layer). With such an arrangement, thelow-refractive-index Al_(x)Ga_(1-x)As layer “f₂” constituting thelight-reflecting layer becomes an AlO_(y) layer having an even lowerrefractive index, so that the reflectance for the light emitted by thelight-emitting layer can be enhanced. Thus, a high reflectance can beobtained even with a small number of pairs in the light-reflectinglayer, and the light emitted from the light-emitting layer can beextracted outside effectively. For example, as shown in FIG. 4,according to the present invention, a higher reflectance can be obtainedas compared with the case where the Al_(x)Ga_(1-x)As layer is notchanged into the AlO_(y) layer (prior art), and yet the half-value widthof the reflection spectrum can be increased. As a result, even withvariations or fluctuations in layer thickness of the light-reflectinglayer, reflectance and reflection spectrum are less liable tovariations, hence a high mass productivity.

FIG. 5 shows a pair-number dependence of the reflectance of thelight-reflecting layer according to the present invention, in comparisonwith prior arts. According to the present invention, thelight-reflecting layer, by virtue of its large refractive indexdifference, can achieve a reflectance of almost 100% even with a fewpairs of the light-reflecting layer. Thus, the growth time can bereduced and a high mass productivity can be obtained.

In one embodiment, there is provided a method for manufacturing asemiconductor light-emitting device, including the steps of making partof the Al_(x)Ga_(1-x)As layer in the layer direction changed into anAlO_(y) layer, and thereafter removing the AlO_(y) layer.

In the semiconductor light-emitting device manufacturing method of thisone embodiment, since the space region formed by the removal of theAlO_(y) layer has a refractive index of 1, a nearly total reflectionstate can be obtained at the chip peripheral portion on the rear side ofthe light-emitting layer. Thus, the light emitted from thelight-emitting layer can be extracted outside effectively.

In one embodiment, there is provided a method for manufacturing asemiconductor light-emitting device, including the step of forming anelectrode for electrical conduction at a region above the light-emittinglayer corresponding to a remaining portion of the Al_(x)Ga_(1-x)As layerthat is not changed into the AlO_(y) layer.

In the semiconductor light-emitting device manufacturing method of thisone embodiment, an electrode is formed at a region above thelight-emitting layer corresponding to a remaining portion of theAl_(x)Ga_(1-x)As layer that is not changed into the AlO_(y) layer.Therefore, out of the Al_(x)Ga_(1-x)As layer, the region correspondingto the portion that has been changed into the AlO_(y) layer can beprevented from being occupied by the electrode. Thus, the lightgenerated by the light-emitting layer and reflected by the AlO_(y) layercan be extracted outside effectively without being interrupted by theelectrode.

In one embodiment, there is provided a method for manufacturing asemiconductor light-emitting device, comprising the steps of forming acurrent blocking layer for blocking electric current at a region abovethe light-emitting layer corresponding to a remaining portion of theAl_(x)Ga_(1-x)As layer that is not changed into the AlO_(y) layer.

In the semiconductor light-emitting device manufacturing method of thisone embodiment, a current blocking layer for blocking electric currentis formed at a region above the light-emitting layer corresponding to aremaining portion of the Al_(x)Ga_(1-x)As layer that is not changed intothe AlO_(y) layer. Therefore, a larger amount of electric current flowsthrough the region corresponding to the AlO_(y) layer, as compared withthe case where the current blocking layer is not formed. Thus, the lightgenerated by the light-emitting layer and reflected by the AlO_(y) layercan be extracted outside effectively.

In one embodiment, there is provided a method for manufacturing asemiconductor light-emitting device, including the steps of forming thelight-reflecting layer by alternately stacking an Al_(x)Ga_(1-x)As layerhaving a specified Al composition (where 0<x≦1) and an AlO_(y) layer,wherein thickness of one layer which is among the Al_(x)Ga_(1-x)Aslayers forming the light-reflecting layer and which is adjacent to theAl_(x)Ga_(1-x)As layer changed into the AlO_(y) layer is set to aquarter of the wavelength.

In the semiconductor light-emitting device manufacturing method of thisone embodiment, the reflectance for the light emitted by thelight-emitting layer is further enhanced at the region corresponding tothe AlO_(y) layer.

In one embodiment, there is provided a method for manufacturing asemiconductor light-emitting device, including the step of forming thelight-emitting layer from an (Al_(x)Ga_(1-x))_(v)In_(1-v)P-basedmaterial.

In the semiconductor light-emitting device manufacturing method of thisone embodiment, a semiconductor light-emitting device having an emissionwavelength band of 560 nm to 650 nm is fabricated.

In one embodiment, there is provided a method for manufacturing asemiconductor light-emitting device, further including the step of,after dividing the layers into chips, making the Al_(x)Ga_(1-x)As layerchanged into the AlO_(y) layer from its exposed end face, where aremaining portion of the Al_(x)Ga_(1-x)As layer that is not changed intothe AlO_(y) layer is made coincident in configuration with the electrodeabove the light-emitting layer.

In the semiconductor light-emitting device manufacturing method of thisone embodiment, since the Al_(x)Ga_(1-x)As layer is changed into theAlO_(y) layer from its exposed end face, the AlO_(y) layer can be formedstably and easily, hence a high mass productivity. Still, since theremaining portion of the Al_(x)Ga_(1-x)As layer that is not changed intothe AlO_(y) layer is made coincident in configuration with the electrodeon the light-emitting layer, the region out of the Al_(x)Ga_(1-x)Aslayer corresponding to the portion that has been changed into theAlO_(y) layer can be prevented from being occupied by the electrode.Thus, the light generated by the light-emitting layer and reflected bythe AlO_(y) layer can be extracted outside effectively without beinginterrupted by the electrode.

In one embodiment, there is provided a method for manufacturing asemiconductor light-emitting device, further including the step of,after dividing the layers into chips, making the Al_(x)Ga_(1-x)As layerchanged into the AlO_(y) layer from its exposed end face, where aremaining portion of the Al_(x)Ga_(1-x)As layer that is not changed intothe AlO_(y) layer is made coincident in configuration with the currentblocking layer.

In the semiconductor light-emitting device manufacturing method of thisone embodiment, since the Al_(x)Ga_(1-x)As layer is changed into theAlO_(y) layer from its exposed end face, the AlO_(y) layer can be formedstably and easily, hence a high mass productivity. Still, since theremaining portion of the Al_(x)Ga_(1-x)As layer that is not changed intothe AlO_(y) layer is made coincident in configuration with the currentblocking layer, a large amount of electric current flows through theregion corresponding to the AlO_(y) layer. Thus, the light generated bythe light-emitting layer and reflected by the AlO_(y) layer can beextracted outside effectively.

In one embodiment, there is provided a method for manufacturing asemiconductor light-emitting device, wherein an Al_(x)Ga_(1-x)P layer,an Al_(x)In_(1-x)P layer or an Al_(x)In_(1-x)As layer is used in placeof the Al_(x)Ga_(1-x)As layer.

Also, as a method for manufacturing a semiconductor light-emittingdevice according to the present invention, there is provided asemiconductor light-emitting device manufacturing method including thestep of providing above a semiconductor substrate a light-emitting layerwhich generates light of a specified wavelength. The method furtherincludes the steps of: depositing on the semiconductor substrate, in anorder given below, a light-reflecting layer in which an Al_(x)Ga_(1-x)Aslayer (where 0<x≦1) having a specified Al composition and an(Al_(x)Ga_(1-x))_(v)In_(1-v)P layer (where 0<x≦1 and 0<v<1) arealternately stacked and which serves for reflecting the light of thewavelength, and the light-emitting layer; and making part of theAl_(x)Ga_(1-x)As layer in the layer direction changed into an AlO_(y)layer (where y is a positive real number).

In the semiconductor light-emitting device manufacturing method of thisinvention, by changing the Al_(x)Ga_(1-x)As layer into an AlO_(y) layerso that the refractive index is lowered, the reflectance for the lightemitted by the light-emitting layer can be enhanced. Thus, a highreflectance can be obtained even with a small number of pairs in thelight-reflecting layer, and the light emitted from the light-emittinglayer can be extracted outside effectively.

Also, the AlO_(y) layer, because of being an oxide, is large in bandgap, and transparent to visible light regions, particularly a region of560 nm to 670 nm, which is the emission region of(Al_(x)Ga_(1-x))_(v)In_(1-v)P-based materials. Therefore, according tothe present invention, a high-quality light-reflecting layer which isvery small in wavelength dependence and which is close to 100% inreflectance can be formed. As a result of this, it is no longernecessary to laboriously select an Al composition which is free fromabsorption to emission wavelength, as would be involved in thelight-reflecting layer made of semiconductor materials of the prior art.

In one embodiment, there is provided a method for manufacturing asemiconductor light-emitting device, further including the step of,after the step of making part of the Al_(x)Ga_(1-x)As layer in the layerdirection changed into an AlO_(y) layer, removing the AlO_(y) layer byusing a hydrofluoric acid-based etching solution.

In the semiconductor light-emitting device manufacturing method of thisone embodiment, only the AlO_(y) layer can be selectively etched andthereby removed out of Al_(x)Ga_(1-x)As layer or the like.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a view for explaining a first principle of the presentinvention;

FIG. 2 is a chart showing a reflection spectrum of the light-reflectinglayer by the first principle;

FIG. 3 is a view for explaining a second principle of the presentinvention;

FIG. 4 is a chart showing a reflection spectrum of the light-reflectinglayer by the second principle;

FIG. 5 is a chart showing pair-number dependence of the reflectance ofthe light-reflecting layer according to the present invention;

FIG. 6 is a sectional view showing the constitution of an LED accordingto a first embodiment of the invention;

FIG. 7 is a sectional view showing the constitution of an LED accordingto a second embodiment of the invention;

FIG. 8 is a sectional view showing the constitution of an LED accordingto a fourth embodiment of the invention;

FIG. 9 is a sectional view showing the constitution of an LED accordingto a fifth embodiment of the invention;

FIG. 10 is a sectional view showing an LED according to a comparativeexample;

FIG. 11 is a sectional view showing the constitution of an LED accordingto a prior art;

FIG. 12 is a sectional view showing the constitution of an LED accordingto another prior art;

FIGS. 13A and 13B are charts showing pair-number dependences of thereflectance of the light-reflecting layer in an LED of the prior art;

FIG. 14 is a view showing an LED lamp made up with the use of thesemiconductor light-emitting device according to the present invention;and

FIG. 15 is a view showing an electric circuit of a display panel made upwith the use of the semiconductor light-emitting device according to thepresent invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Hereinbelow, the present invention is described in detail by way ofembodiments thereof illustrated in the accompanying drawings.

First Embodiment

FIG. 6 shows a cross-sectional structure of a semiconductor LEDaccording to a first embodiment. This embodiment is characterized inthat main reflecting part of a first light-reflecting layer is given byan AlO_(y) single layer (where y is a positive real number).

This LED includes, on an n-type GaAs substrate 1, an n-type GaAs bufferlayer (e.g., thickness: 0.5 μm; dopant concentration: 5×10¹⁷ cm⁻³) 2, ann-type AlAs conductive layer 3 as a sub reflecting part and an AlO_(y)oxide layer 13 as a main reflecting part, which adjoin along the layerdirection as a first light-reflecting layer. The n-type AlAs conductivelayer 3 as the sub reflecting part is disposed at a center region of thechip, and the AlO_(y) oxide layer 13 as the main reflecting part isdisposed at a peripheral region of the chip so as to surround theconductive layer 3. This LED further includes thereon an(Al_(x)Ga_(1-x))_(0.51)In_(0.49)P lower cladding layer (0≦x≦1, e.g.x=1.0; thickness: 1.0 μm; dopant concentration: 5×10¹⁷ cm⁻³) 5, a p-type(Al_(x)Ga_(1-x))_(v)In_(1-v)P active layer (0≦x≦1, e.g. x=0.42;thickness: 0.6 μm; dopant concentration: 1×10¹⁷ cm⁻³) 6; a p-type(Al_(x)Ga_(1-x))_(0.51)In_(0.49)P upper cladding layer (0≦x≦1, e.g.x=1.0; thickness: 1.0 μm; dopant concentration: 5×10¹⁷ cm⁻³) 7, and ap-type (Al_(x)Ga_(1-x))_(v)In_(1-v)P intermediate layer (x=0.2; v=0.4;thickness: 0.15 μm; dopant concentration: 1×10¹⁸ cm⁻³) 8, in this order.This LED includes further thereon a p-type (Al_(x)Ga_(1-x))_(v)In_(1-v)Pcurrent spreading layer (x=0.05; v=0.05; total thickness: 8.5 μm; dopantconcentration: 5×10¹⁸ cm⁻³) 10, and an n-type GaP current blocking layer(thickness: 0.3 μm; dopant concentration: 1×10¹⁸ cm⁻³) 9 which is formedat a central region in this current spreading layer and which serves toblock electric current. Reference numeral 11 denotes an n-sideelectrode, and 12 denotes a p-side electrode.

This LED is fabricated by the following process:

(i) All over an n-type GaAs substrate 1, are deposited, in an ordergiven below, an n-type GaAs buffer layer (e.g., thickness: 0.5 μm;dopant concentration: 5×10¹⁷ cm⁻³) 2, an n-type AlAs conductive layer 3as an Al rich layer, an (Al_(x)Ga_(1-x))_(0.51)In_(0.49)P lower claddinglayer (0≦x≦1, e.g. x=1.0; thickness: 1.0 μm; dopant concentration:5×10¹⁷ cm⁻³) 5; a p-type (Al_(x)Ga_(1-x))_(v)In_(1-v)P active layer(0≦x≦1, e.g. x=0.42; thickness: 0.6 μm; dopant concentration: 1×10¹⁷cm⁻³) 6 as an active layer; a p-type (Al_(x)Ga_(1-x))_(0.51)In_(0.49)Pupper cladding layer (0≦x≦1, e.g. x=1.0; thickness: 1.0 μm; dopantconcentration: 5×10¹⁷ cm⁻³) 7, and a p-type(Al_(x)Ga_(1-x))_(v)In_(1-v)P intermediate layer (x=0.2; v=0.4;thickness: 0.15 μm; dopant concentration: 1×10¹⁸ cm⁻³) 8.

(ii) Next, on the p-type (Al_(x)Ga_(1-x))_(v)In_(1-v)P intermediatelayer 8, are grown a p-type (Al_(x)Ga_(1-x))_(v)In_(1-v)P currentspreading layer (x=0.05; v=0.05; thickness: 1.5 μm; dopantconcentration: 5×10¹⁸ cm⁻³) 10, and further thereon an n-type GaPcurrent blocking layer (thickness: 0.3 μm; dopant concentration: 1×10¹⁸cm⁻³) 9. Thereafter, the n-type GaP current blocking layer 9 issubjected to selective etching by photolithography process so as to bepatterned into an M=100 μm square to 150 μm square, with a current pathfor applied electric current formed therearound. Subsequently, a p-type(Al_(x)Ga_(1-x))_(v)In_(1-v)P current spreading layer (x=0.05; v=0.05;thickness: 7 μm; dopant concentration 5×10¹⁸ cm⁻³) 10 is regrown.

(iii) Next, a metal layer to serve as an electrode is provided on the pside, and subject to selective etching by photolithography so that theelectrode 12 is patterned into an M=100 μm square to 150 μm square inalignment with the position of the current blocking layer 9. Thereafter,the substrate 1 is thinly polished to a thickness of about 120 μm fromits rear face side, and an electrode 11 is formed also on the n side(the substrate in this state is called wafer, normally about 50 mm dia.sized). As in the normal breaking method, this wafer, after stuck on itsrear face side to an adhesive sheet, is groove-cut halfway of thethickness of the wafer along the pattern of the electrode 12 with adicing saw, and then spread by pulling up the adhesive sheet. Thus, thewafer is divided into L=280 μm square chips.

(iv) Dividing into chips causes the AlAs layer 3 to be exposed at thechip side faces. In this state, the chips are thrown into oxide formingequipment (not shown) provided in a nitrogen atmosphere at 400° C.Nitrogen gas that has been passed through boiling water is let into theinterior of the oxide forming equipment, so that the oxide formingequipment is internally filled with high-temperature steam. When thehigh-temperature steam is introduced to the side faces at which the AlAslayer 3 is exposed, oxidation progresses at a constant speed from endportions of the chip side faces to their interiors, allowing peripheralportions of the original AlAs layer 3 to be changed into the AlO_(y)layer 13 (e.g., Specification of U.S. Pat. No. 5,517,039, or Kenichi Igaet al., “Fundamentals and Applications of Plane Emission Laser,”Kyoritsu Shuppan K. K., June 1999, pp. 105-113.) A layer-direction size(depth of oxidation) N of this AlO_(y) layer 13 depends on thetemperature, time and material of this oxidation.

The oxidation is further characterized in that better-quality oxide filmcan be obtained when oxidation is done by steam than merely by oxygen.In particular, bringing steam into a thermostatic oven by nitrogen gasis intended to keep oxygen from entering.

This layer-direction size N is desirably set so as to satisfy thecondition:N≦(L−M)/2,where L is the chip size and M is the length of one side of the currentblocking layer or electrode. In this embodiment, the chips are kept inthe oxide forming equipment at 400° C. for 3 hours so that thelayer-direction size N of the AlO_(y) layer 13 becomes 80 μm. Whereasthe refractive index of the original AlAs layer 3 is 3.1, the refractiveindex of the AlO_(y) layer 13 resulting from the oxidation is as low as1.9. Whereas the reflectance at the substrate is about 30% in the priorart, the reflectance of the light-reflecting layer at peripheral regionsof the chips was able to be improved to 80% or more in this embodiment.

Also, when the AlAs layer 3 exposed is oxidized from end portions of thechip side faces so that the peripheral portion of the original AlAslayer 3 is changed into the AlO_(y) layer 13 as shown above, the AlO_(y)layer can be formed stably and easily, with high mass-productivity.Still, since the remaining portion of the AlAs layer 3 that is notchanged into the AlO_(y) layer is made coincident in configuration withthe current blocking layer 9, a larger amount of electric current flowsthrough the peripheral region of the chip corresponding to the AlO_(y)layer 13. Therefore, a larger amount of light is generated at aperipheral portion 6 a of the active layer 6. Since reflectance of thelight-reflecting layer is improved at peripheral regions of the chips,the light generated at the peripheral portion 6 a of the active layer 6is reflected at higher efficiency. More concretely, 80% or more of light90 reflected from the active layer 6 toward the rear face (substrate)side can be reflected toward the top face side by the AlO_(y) layer 13.Then, the light reflected toward the top face side is extracted outsideeffectively without being interrupted by the electrode 12. Actually, inthis embodiment, chip luminous intensity at the emission wavelength of570 nm was able to be improved from normal 35 mcd to 50 mcd. Thus, animprovement in brightness was achieved and an improvement in yield wasalso obtained.

COMPARATIVE EXAMPLE

FIG. 10 shows a semiconductor LED having a structure in which thecurrent blocking layer 9 is omitted, as a comparative example. Exceptthat the n-type GaP current blocking layer 9 is omitted, thissemiconductor LED is utterly identical in structure to the semiconductorLED of the first embodiment, i.e., absolutely identical in terms ofthickness, composition and conductive type of the individual layers.

However, with the semiconductor LED of this comparative example, thebrightness-improvement effect was not able to obtain. The reason of thiscould be considered as follows. That is, in the semiconductor LED ofthis comparative example, since there is no current blocking layer justunder the electrode 12 and since the AlO_(y) layer 13 is an insulatinglayer, the emission region is limited to a central portion 6 b (aportion just under the electrode 12) of the active layer 6. In thiscase, out of the light radiated from the central portion 6 b of theactive layer 6 toward the rear face (substrate) side, a slight portion90B thereof goes ahead to the peripheral region of the chip so as to bereflected toward the top face side by the AlO_(y) layer 13, whereas mostpart 90C thereof becomes incident on the conductive layer 3 justthereunder so as to be absorbed to the substrate without being reflectedtoward the top face side and, even if reflected toward the top faceside, interrupted by the p-type electrode 12 and not extracted tooutside. As a result, the emission efficiency cannot be improved, and noimprovement in brightness can be obtained. Actually, in this comparativeexample, the chip luminous intensity at the emission wavelength of 570nm lowered to 10 mcd, on the contrary, compared with 35 mcd of theconventional structure.

Second Embodiment

FIG. 7 shows a cross-sectional structure of a semiconductor LEDaccording to a second embodiment. This embodiment is characterized inthat a main reflecting part of the first light-reflecting layer isformed of a multilayer film in which a pair of AlO_(y) layer and AlGaAslayer are alternately stacked to a plurality of pairs.

This LED includes, on an n-type GaAs substrate 1, an n-type GaAs bufferlayer (e.g., thickness: 0.5 μm; dopant concentration: 5×10¹⁷ cm⁻³) 2, ann-type AlAs/Al_(x)Ga_(1-x)As conductive-type light-reflecting layer(e.g., x=0.65; dopant concentration: 5×10¹⁷ cm⁻³) 15 as a sub reflectingpart and an AlO_(y)/Al_(x)Ga_(1-x)As oxide light-reflecting layer 14 asa main reflecting part, which adjoin along the layer direction as afirst light-reflecting layer. The n-type AlAs/Al_(x)Ga_(1-x)Asconductive-type light-reflecting layer 15 as the sub reflecting part isdisposed at a center region of the chip, and theAlO_(y)/Al_(x)Ga_(1-x)As oxide light-reflecting layer 14 as the mainreflecting part is disposed at a peripheral region of the chip so as tosurround the conductive-type light-reflecting layer 15. This LED furtherincludes thereon an (Al_(x)Ga_(1-x))_(0.51)In_(0.49)P lower claddinglayer (0≦x≦1, e.g. x=1.0; thickness: 1.5 μm; dopant concentration:5×10¹⁷ cm⁻³) 5, a p-type (Al_(x)Ga_(1-x))_(v)In_(1-v)P active layer(e.g., x=0.42; thickness: 0.6 μm; dopant concentration: 1×10¹⁷ cm⁻³) 6;a p-type (Al_(x)Ga_(1-x))_(0.51)In_(0.49)P upper cladding layer (0≦x≦1,e.g. x=1.0; thickness: 1.0 μm; dopant concentration: 5×10¹⁷ cm⁻³) 7, anda p-type (Al_(x)Ga_(1-x))_(v)In_(1-v)P intermediate layer (x=0.2; v=0.4;thickness: 0.15 μm; dopant concentration: 1×10¹⁸ cm⁻³) 8, in this order.This LED includes further thereon a p-type (Al_(x)Ga_(1-x))_(v)In_(1-v)Pcurrent spreading layer (x=0.05; v=0.05; total thickness: 8.5 μm; dopantconcentration: 5×10¹⁸ cm⁻³) 10, and an n-type GaP current blocking layer(thickness: 0.3 μm; dopant concentration: 1×10¹⁸ cm⁻³) 9 which is formedat a central region in this current spreading layer and which serves toblock electric current. Reference numeral 11 denotes an n-sideelectrode, and 12 denotes a p-side electrode.

This LED is fabricated by the following process:

(i) All over an n-type GaAs substrate 1, are deposited, in an ordergiven below, an n-type GaAs buffer layer (e.g., thickness: 0.5 μm;dopant concentration: 5×10¹⁷cm⁻³) 2, an n-type AlAs/Al_(x)Ga_(1-x)Asconductive-type light-reflecting layer (e.g., x=0.65; dopantconcentration: 5×10¹⁷ cm⁻³) 15, an (Al_(x)Ga_(1-x))_(0.51)In_(0.49)Plower cladding layer (0≦x≦1, e.g. x=1.0; thickness: 1.5 μm; dopantconcentration: 5×10¹⁷ cm⁻³) 5; a p-type (Al_(x)Ga_(1-x))_(v)In_(1-v)Pactive layer (e.g., x=0.42; thickness: 0.6 μr; dopant concentration:1×10¹⁷ cm⁻³) 6; a p-type (Al_(x)Ga_(1-x))_(0.51)In_(0.49)P uppercladding layer (0≦x≦1, e.g. x=1.0; thickness: 1.0 μm; dopantconcentration: 5×10¹⁷ cm⁻³) 7, and a p-type(Al_(x)Ga_(1-x))_(v)In_(1-v)P intermediate layer (x=0.2; v=0.4;thickness: 0.15 μm; dopant concentration: 1×10¹⁸ cm⁻³) 8.

It is noted here that the n-type AlAs/Al_(x)Ga_(1-x)As conductive-typelight-reflecting layer 15 is made up by stacking alternately AlAs layer15 ₂ as an Al rich layer and Al_(x)Ga_(1-x)As layer 15 ₁.

(ii) Next, on the p-type (Al_(x)Ga_(1-x))_(v)In_(1-v)P intermediatelayer 8, are grown a p-type (Al_(x)Ga_(1-x))_(v)In_(1-v)P currentspreading layer (x=0.05; v=0.05; thickness: 1.5 μm; dopantconcentration: 5×10¹⁸ cm⁻³) 10, and further thereon an n-type GaPcurrent blocking layer (thickness: 0.3 μm; dopant concentration: 1×10¹⁸cm⁻³) 9. Thereafter, the n-type GaP current blocking layer 9 issubjected to selective etching by photolithography process so as to bepatterned into an M=100 μm square to 150 μm square, with a current pathfor applied electric current formed therearound. Subsequently, a p-type(Al_(x)Ga_(1-x))_(v)In_(1-v)P current spreading layer (x=0.05; v=0.05;thickness: 7 μm; dopant concentration 5×10¹⁸ cm⁻³) 10 is regrown.

(iii) Next, a metal layer to serve as an electrode is provided on the pside, and subject to selective etching by photolithography so that theelectrode 12 is patterned into an M=100 μm square to 150 μm square inalignment with the position of the current blocking layer 9. Thereafter,the substrate 1 is thinly polished to a thickness of about 120 μm fromits rear face side, and an electrode 11 is formed also on the n side.Then, in the same manner as in the first embodiment, the wafer isdivided into L=280 μm square chips.

(iv) Subsequently, the chip side faces are exposed to the air, andthereafter the individual AlAs layers 15 ₂ constituting the n-typeAlAs/Al_(x)Ga_(1-x)As conductive-type light-reflecting layer 15 areoxidized from the end portions of the side faces in the same manner asin the first embodiment, thereby making peripheral portions of theoriginal AlAs layers 15 ₂ changed into AlO_(y) layers 14 ₂,respectively. That is, peripheral portion out of the original n-typeAlAs/Al_(x)Ga_(1-x)As conductive-type light-reflecting layer 15 ischanged into an AlO_(y)/Al_(x)Ga_(1-x)As oxide light-reflecting layer 14having a structure in which AlO_(y) layer 14 ₂ as a low-refractive-indexmaterial layer and Al_(x)Ga_(1-x)As layer 15 ₁ (this is expressed as “14₁” in the figure) as a high-refractive-index material layer arealternately stacked to a plurality. The layer-direction size (depth ofoxidation) N of this AlO_(y)/Al_(x)Ga_(1-x)As oxide light-reflectinglayer 14 depends on the temperature and time of this oxidation. Thislayer-direction size N, as in the first embodiment, is desirably set soas to satisfy the condition:N≦(L−M)/2,where L is the length of one side of the chip size and M is the lengthof one side of the current blocking layer or electrode. In thisembodiment, as in the first embodiment, the chips are kept in the oxideforming equipment at 400° C. for 3 hours so that the layer-directionsize N of the AlO_(y)/Al_(x)Ga_(1-x)As oxide light-reflecting layer 14becomes 80 μm. As to the refractive index of the resultingAlO_(y)/Al_(x)Ga_(1-x)As oxide light-reflecting layer 14, the refractiveindex of the AlO_(y) layer 14 ₂ as the low-refractive-index materiallayer is as low as 1.9 (the refractive index of the original AlAs layer15 ₂ is 3.1). Meanwhile, the refractive index of the Al_(x)Ga_(1-x)Aslayer 15 ₁ (i.e. “14 ₁”) as the high-refractive-index material layerremains unchanged, being 3.4. This is because the Al_(x)Ga_(1-x)As layeras the high-refractive-index material layer, whose Al composition of 0.6is lower as compared with AlAs, is transformed into oxide only at itsportions around side-face end portions of the chip under the aboveconditions.

As shown above, the resulting AlO_(y)/Al_(x)Ga_(1-x)As oxidelight-reflecting layer 14 becomes a distributed Bragg reflector layerhaving a large refractive index difference of 1.5 betweenlow-refractive-index material layer and high-refractive-index materiallayer. Whereas 10 pairs of low-refractive-index material layer andhigh-refractive-index material layer generally yield aphotoreflection-layer reflectance of about 55%, only 5 pairs yielded aphotoreflection-layer reflectance of 99% in this embodiment.

Also, when the individual AlAs layers constituting the n-typeAlAs/Al_(x)Ga_(1-x)As conductive-type light-reflecting layer 15 areoxidized from side-face end portions as shown above, the distributedBragg light-reflecting layer 14 can be formed stably and easily atperipheral regions of the chips, with high mass-productivity. Still,since the remaining portion of the original n-type AlAs/Al_(x)Ga_(1-x)Asconductive-type light-reflecting layer 15 that is not changed into theAlO_(y) layer is made coincident in configuration with the currentblocking layer 9, a larger amount of electric current flows through theperipheral region of the chip corresponding to theAlO_(y)/Al_(x)Ga_(1-x)As oxide light-reflecting layer 14. Therefore, alarger amount of light is generated at a peripheral portion 6 a of theactive layer 6. Since reflectance of the light-reflecting layer isimproved at peripheral regions of the chips, light 90 generated at theperipheral portion 6 a of the active layer 6 is reflected at highefficiency so as to be extracted outside effectively without beinginterrupted by the electrode 12. Actually, in this embodiment, chipluminous intensity at the emission wavelength of 570 nm was able to beimproved from normal 35 mcd to 60 mcd. Further, the half-value width ofthe reflection spectrum increased fivefold or more, compared with thehalf-value width of about 20 nm of normal light-reflecting layers. Thus,even with variations in layer thickness of the light-reflecting layer 15in mass production, reflectance and reflection spectrum were less liableto variations, so that the uniformity of luminous intensity was improvedand the yield was also improved.

Third Embodiment

An LED of the third embodiment, which is not shown, is characterized inthat the material of the first light-reflecting layer in thesemiconductor light-emitting device of the second embodiment shown inFIG. 7 is changed.

The LED of this embodiment includes an n-typeAlInP/(Al_(x)Ga_(1-x))_(v)In_(1-v)P conductive-type light-reflectinglayer as a sub reflecting part and an n-typeAlO_(y)/(Al_(x)Ga_(1-x))_(v)In_(1-v)P oxide light-reflecting layer as amain reflecting part, which adjoin along the layer direction as a firstlight-reflecting layer. The rest of the constituent elements are thesame as in the semiconductor light-emitting device of the secondembodiment.

In this case, the n-type AlInP/(Al_(x)Ga_(1-x))_(v)In_(1-v)Pconductive-type light-reflecting layer as the sub reflecting part ismade up as a distributed Bragg reflector layer by stacking a pair ofAlInP layer and (Al_(x)Ga_(1-x))_(v)In_(1-v)P layer to a plurality.Thicknesses of the AlInP layer and the (Al_(x)Ga_(1-x))_(v)In_(1-v)Player constituting each pair are each set so as to become a quarter ofthe emission wavelength λ.

The LED of this embodiment is fabricated by the same procedure as in thecase of the LED of the second embodiment. In particular, the individualn-type AlO_(y) layers included in the main reflecting part of the firstlight-reflecting layer are formed by setting the individual AlInP layersincluded in the sub reflecting part into oxide forming equipment, andoxidizing them from end-face side portions of the chips as in the firstembodiment. Whereas the refractive index of the original AlInP layer 3is 3.1, the refractive index of the AlO_(y) layer 13 resulting from theoxidation is as low as 1.9. Whereas the reflectance of thelight-reflecting layer is about 50% in the prior art, the reflectance ofthe light-reflecting layer at peripheral regions of the chips was ableto be improved to 99% or more in this embodiment.

In the case where the material to be oxidized is AlInP as in thisembodiment, oxidation progresses slower than in the case where thematerial to be oxidized is the AlAs layer. However, adopting GaInP asthe other material to be paired allows prolonged time to be taken forthe oxidization, because GaInP is not oxidized at all. As a result, abetter controllability for the layer-direction size (depth of oxidation)N of oxidized portions can be obtained. Further, the half-value width ofthe reflection spectrum increased threefold or more, compared with thehalf-value width (about 20 nm) of normal light-reflecting layers. Thus,even with variations in layer thickness of the individual layersconstituting the first light-reflecting layer in mass production,reflectance and reflection spectrum are less liable to variations. As aresult of this, the uniformity of luminous intensity was improved andthe yield was also improved.

Fourth Embodiment

FIG. 8 shows a cross-sectional structure of a semiconductor LEDaccording to a fourth embodiment. This embodiment is characterized inthat the main reflecting part of the first light-reflecting layer isformed of space.

This LED includes, on an n-type GaAs substrate 1, an n-type GaAs bufferlayer (e.g., thickness: 0.5 μm; dopant concentration: 5×10¹⁷ cm⁻³) 2, ann-type AlAs conductive layer 16 as a sub reflecting part and a spaceregion 17 as a main reflecting part, which adjoin along the layerdirection as a first light-reflecting layer. The n-type AlAs conductivelayer 16 as the sub reflecting part is disposed at a center region ofthe chip, and the space region 17 as the main reflecting part isdisposed at a peripheral region of the chip so as to surround theconductive layer 16. In other words, this embodiment is an embodiment inwhich the first light-reflecting layer is so formed that a portion ofthe n-type AlAs conductive layer 16 corresponding to the chip peripheryis removed from an all-over stacked n-type AlAs conductive layer 16.This LED further includes thereon an (Al_(x)Ga_(1-x))_(0.51)In_(0.49)Plower cladding layer (0≦x≦1, e.g. x=1.0; thickness: 1.0 μm; dopantconcentration: 5×10¹⁷ cm⁻³) 5, a p-type (Al_(x)Ga_(1-x))_(v)In_(1-v)Pactive layer (e.g. x=0.42; thickness: 0.6 μm; dopant concentration:1×10¹⁷ cm⁻³) 6; a p-type (Al_(x)Ga_(1-x))_(0.51)In_(0.49)P uppercladding layer (0≦x≦1, e.g. x=1.0; thickness: 2.0 μm; dopantconcentration: 5×10¹⁷ cm⁻³) 7, and a p-type(Al_(x)Ga_(1-x))_(v)In_(1-v)P intermediate layer (x=0.2; v=0.4;thickness: 0.15 μm; dopant concentration: 1×10¹⁸ cm⁻³) 8, in this order.This LED includes further thereon a p-type (Al_(x)Ga_(1-x))_(v)In_(1-v)Pcurrent spreading layer (x=0.05; v=0.05; total thickness: 8.5 μm; dopantconcentration: 5×10¹⁸ cm⁻³) 10, and an n-type GaP current blocking layer(thickness: 0.3 μm; dopant concentration: 1×10¹⁸ cm⁻³) 9 which is formedat a central region in this current spreading layer and which serves toblock electric current. Reference numeral 11 denotes an n-sideelectrode, and 12 denotes a p-side electrode.

This LED is fabricated by the following process:

(i) All over an n-type GaAs substrate 1, are deposited, in an ordergiven below, an n-type GaAs buffer layer (e.g., thickness: 0.5 μm;dopant concentration: 5×10¹⁷ cm⁻³) 2, an n-type AlAs conductive layer 16as an Al rich layer, an (Al_(x)Ga_(1-x))_(0.51)In_(0.49)P lower claddinglayer (0≦x≦1, e.g. x=1.0; thickness: 1.0 μm; dopant concentration:5×10¹⁷ cm⁻³) 5; a p-type (Al_(x)Ga_(1-x))_(v)In_(1-v)P active layer(e.g. x=0.42; thickness: 0.6 μm; dopant concentration: 1×10¹⁷ cm⁻³) 6; ap-type (Al_(x)Ga_(1-x))_(0.51)In_(0.49)P upper cladding layer (0≦x≦1,e.g. x=1.0; thickness: 2.0 μm; dopant concentration: 5×10¹⁷ cm⁻³) 7, anda p-type (Al_(x)Ga_(1-x))_(v)In_(1-v)P intermediate layer (x=0.2; v=0.4;thickness: 0.15 μm; dopant concentration: 1×10¹⁸ cm⁻³) 8.

(ii) Next, on the p-type (Al_(x)Ga_(1-x))_(v)In_(1-v)P intermediatelayer 8, are grown a p-type (Al_(x)Ga_(1-x))_(v)In_(1-v)P currentspreading layer (x=0.05; v=0.05; thickness: 1.5 μm; dopantconcentration: 5×10¹⁸ cm⁻³) 10, and further thereon an n-type GaPcurrent blocking layer (thickness: 0.3 μm; dopant concentration: 1×10¹⁸cm⁻³) 9. Thereafter, the n-type GaP current blocking layer 9 issubjected to selective etching by photolithography process so as to bepatterned into an M=100 μm square to 150 μm square, with a current pathfor applied electric current formed therearound. Subsequently, a p-type(Al_(x)Ga_(1-x))_(v)In_(1-v)P current spreading layer (x=0.05; v=0.05;thickness: 7 μm; dopant concentration 5×10¹⁸ cm⁻³) 10 is regrown.

(iii) Next, a metal layer to serve as an electrode is provided on the pside, and subject to selective etching by photolithography so that theelectrode 12 is patterned into an M=100 μm square to 150 μm square inalignment with the position of the current blocking layer 9. Thereafter,the substrate 1 is thinly polished to a thickness of about 120 μm fromits rear face side, and an electrode 11 is formed also on the n side(the substrate in this state is called wafer, normally about 50 mm dia.sized). Then, in the same manner as in the first embodiment, the waferis divided into L=280 μm square chips.

(iv) Subsequently, the chip side faces are exposed to the air, andthereafter the AlAs layer 16 is oxidized from the end portions of theside faces in the same manner as in the first embodiment, thereby makingperipheral portions of the original AlAs layer 16 changed into AlO_(y)layers, respectively. The layer-direction size (depth of oxidation) N ofthis AlO_(y)/Al_(x)Ga_(1-x)As oxide light-reflecting layer 14 depends onthe temperature and time of this oxidation. This layer-direction size N,as in the first embodiment, is desirably set so as to satisfy thecondition:N≦(L−M)/2,where L is the length of one side of the chip size and M is the lengthof one side of the current blocking layer or electrode. In thisembodiment, the chips are kept in the oxide forming equipment at 400° C.for 3 hours so that the layer-direction size N of the AlO_(y) layerbecomes 80 μm. Whereas the refractive index of the originalsemiconductor layer is 2.9 to 3.5, the refractive index of the AlO_(y)layer resulting from the oxidation is as low as 1.9.

(v) In this embodiment, in order to obtain a further lower reflectance,only the AlO_(y) layer formed at a peripheral portion of the originalAlAs conductive layer 16 is selectively etched with hydrofluoric acid orammonium fluoride solution or hydrofluoric acid diluted twofold totenfold, and thereby removed, in the chip state.

As shown above, this LED is fabricated by the same manufacturing processas the semiconductor light-emitting device of the first embodiment,except that after the oxidation of the AlAs layer 16, the AlO_(y) layerformed at the peripheral portion is removed.

The refractive index of the space region 17 formed by the removal ofAlO_(y) is almost 1, whether the region is in a vacuum or in thepresence of inert gas such as air or nitrogen. Accordingly, a nearlytotal reflection state was able to be obtained at the chip peripheralportion on the rear side of the active layer 6, so that a substantiallyalmost 100% reflectance was able to be obtained.

Actually, in this embodiment, the chip luminous intensity at theemission wavelength of 570 nm was able to be improved from normal 35 mcdto 60 mcd. Further, since the main reflecting part of the firstlight-reflecting layer is the space region 17, which does not need to befilled with any material, the optical reflectance on the rear face sideremains unchanged even if the growth rate is changed due to changes ingrowth conditions. As a result, reflectance and reflection spectrum wereless liable to variations, so that the uniformity of luminous intensitywas improved and the yield was also improved.

Fifth Embodiment

FIG. 9 shows a cross-sectional structure of a semiconductor LEDaccording to a fifth embodiment. This embodiment is characterized inthat a second light-reflecting layer is provided between the firstlight-reflecting layer and the active layer.

This LED includes, on an n-type GaAs substrate 1, an n-type GaAs bufferlayer (e.g., thickness: 0.5 μm; dopant concentration: 5×10¹⁷ cm⁻³) 2, ann-type AlAs conductive layer 3 as a sub reflecting part and an AlO_(y)oxide layer 13 as a main reflecting part, which adjoin along the layerdirection as a first light-reflecting layer. The n-type AlAs conductivelayer 3 as the sub reflecting part is disposed at a center region of thechip, and the AlO_(y) oxide layer 13 as the main reflecting part isdisposed at a peripheral region of the chip so as to surround theconductive layer 3. This LED further includes thereon an n-typeAlInP/(Al_(x)Ga_(1-x))_(v)In_(1-v)P light-reflecting layer 4 as a secondlight-reflecting layer. This light-reflecting layer 4 is made up bystacking a pair of an AlInP layer 42 as a low-refractive-index materiallayer and an (Al_(x)Ga_(1-x))_(v)In_(1-v)P layer 4 ₁ as ahigh-refractive-index material layer alternately to a plurality as adistributed Bragg reflector layer. As in the first embodiment ofsemiconductor LED, this LED further includes thereon an(Al_(x)Ga_(1-x))_(0.51)In_(0.49)P lower cladding layer (0≦x≦1, e.g.x=1.0; thickness: 1.0 μm; dopant concentration: 5×10¹⁷ cm⁻³) 5, a p-type(Al_(x)Ga_(1-x))_(v)In_(1-v)P active layer (0≦x≦1, e.g. x=0.42;thickness: 0.6 μm; dopant concentration: 1×10¹⁷ cm⁻³) 6; a p-type(Al_(x)Ga_(1-x))_(0.51)In_(0.49)P upper cladding layer (0≦x≦1, e.g.x=1.0; thickness: 1.0 μm; dopant concentration: 5×10¹⁷ cm⁻³) 7, and ap-type (Al_(x)Ga_(1-x))_(v)In_(1-v)P intermediate layer (x=0.2; v=0.4;thickness: 0.15 μm; dopant concentration: 1×10¹⁸ cm⁻³) 8, in this order.This LED includes further thereon a p-type (Al_(x)Ga_(1-x))_(v)In_(1-v)Pcurrent spreading layer (x=0.05; v=0.05; total thickness: 8.5 μm; dopantconcentration: 5×10¹⁸ cm⁻³) 10, and an n-type GaP current blocking layer(thickness: 0.3 μm; dopant concentration: 0.1×10¹⁸ cm⁻³) 9 which isformed at a central region in this current spreading layer and whichserves to block electric current. Reference numeral 11 denotes an n-sideelectrode, and 12 denotes a p-side electrode.

This LED is fabricated by the following process:

(i) All over an n-type GaAs substrate 1, are deposited, in an ordergiven below, an n-type GaAs buffer layer (e.g., thickness: 0.5 μm;dopant concentration: 5×10¹⁷ cm⁻³) 2, an n-type AlAs conductive layer 3,an n-type AlInP/(Al_(x)Ga_(1-x))_(v)In_(1-v)P light-reflecting layer 4,an (Al_(x)Ga_(1-x))_(0.51)In_(0.49)P lower cladding layer (0≦x≦1, e.g.x=1.0; thickness: 1.0 μm; dopant concentration: 5×10¹⁷ cm⁻³) 5; a p-type(Al_(x)Ga_(1-x))_(v)In_(1-v)P active layer (0≦x≦1, e.g. x=0.42;thickness: 0.6 μm; dopant concentration: 1×10¹⁷ cm⁻³) 6 as anlight-emitting layer; a p-type (Al_(x)Ga_(1-x))_(0.51)In_(0.49)P uppercladding layer (0≦x≦1, e.g. x=1.0; thickness: 1.0 μm; dopantconcentration: 5×10¹⁷ cm⁻³) 7, and a p-type(Al_(x)Ga_(1-x))_(v)In_(1-v)P intermediate layer (x=0.2; v=0.4;thickness: 0.15 μm; dopant concentration: 1×10¹⁸ cm⁻³) 8.

As already described, the n-type AlInP/(Al_(x)Ga_(1-x))_(v)In_(1-v)Plight-reflecting layer 4 is made up by stacking a pair of AlInP layer 4₂ and (Al_(x)Ga_(1-x))_(v)In_(1-v)P layer 4 ₁ alternately as adistributed Bragg reflector layer. Layer thicknesses of the n-type AlAsconductive layer 3 and the n-type AlInP/(Al_(x)Ga_(1-x))_(v)In_(1-v)Plight-reflecting layer 4 are each set so as to become a quarter of theemission wavelength λ, in principle. However, taking into considerationthat the AlAs conductive layer 3 is oxidized so that the refractiveindex will be lowered in later-described process, only the layer closestto the AlAs conductive layer 3 out of the n-typeAlInP/(Al_(x)Ga_(1-x))_(v)In_(1-v)P light-reflecting layer 4 is set to alayer thickness half the emission wavelength λ.

(ii) Next, on the p-type (Al_(x)Ga_(1-x))_(v)In_(1-v)P intermediatelayer 8, are grown a p-type (Al_(x)Ga_(1-x))_(v)In_(1-v)P currentspreading layer (x=0.05; v=0.05; thickness: 1.5 μm; dopantconcentration: 5×10¹⁸ cm⁻³) 10, and further thereon an n-type GaPcurrent blocking layer (thickness: 0.3 μm; dopant concentration: 1×10¹⁸cm⁻³) 9. Thereafter, the n-type GaP current blocking layer 9 issubjected to selective etching by photolithography process so as to bepatterned into an M=100 μm square to 150 μm square, with a current pathfor applied electric current formed therearound. Subsequently, a p-type(Al_(x)Ga_(1-x))_(v)In_(1-v)P current spreading layer (x=0.05; v=0.05;thickness: 7 μm; dopant concentration 5×10¹⁸ cm⁻³) 10 is regrown.

(iii) Next, a metal layer to serve as an electrode is provided on the pside, and subject to selective etching by photolithography so that theelectrode 12 is patterned into an M=100 μm square to 150 μm square inalignment with the position of the current blocking layer 9. Thereafter,the substrate 1 is thinly polished to a thickness of about 120 μm fromits rear face side, and an electrode 11 is formed also on the n side(the substrate in this state is called wafer, normally about 50 mm dia.sized). Then, in the same manner as in the first embodiment, the waferis divided into L=280 μm square chips.

(iv) Subsequently, the chip side faces are exposed to the air, andthereafter the AlAs layer 3 is oxidized from the end portions of theside faces in the same manner as in the first embodiment, thereby makingperipheral portions of the original AlAs layer 3 changed into AlO_(y)layers 13, respectively. The layer-direction size (depth of oxidation) Nof this AlO_(y)/Al_(x)Ga_(1-x)As oxide light-reflecting layer 14 dependson the temperature and time of this oxidation. This layer-direction sizeN, as in the first embodiment, is desirably set so as to satisfy thecondition:N≦(L−M)/2,where L is the length of one side of the chip size and M is the lengthof one side of the current blocking layer or electrode. In thisembodiment, as in the first embodiment, the chips are kept in the oxideforming equipment at 400° C. for 3 hours so that the layer-directionsize N of the AlO_(y) layer becomes 80 μm.

As shown above, this LED is fabricated by the same manufacturing processas the semiconductor light-emitting device of the first embodiment,except that after the formation of the first light-reflecting layerincluding the AlO_(y) layer 13 as the main reflecting part, the n-typeAlInP/(Al_(x)Ga_(1-x))_(v)In_(1-v)P light-reflecting layer 4 is formedthereon as the second light-reflecting layer.

Whereas the refractive index of the original AlAs layer 3 is 3.1, therefractive index of the AlO_(y) layer 13 resulting from the oxidation isas low as 1.9. Whereas the reflectance of the light-reflecting layer isabout 50% in the prior art, the reflectance of the light-reflectinglayer at the peripheral regions of the chips was able to be improved to99% or more in this embodiment.

Also, when the AlAs layer 3 is oxidized from side-face end portions asshown above so that the peripheral portion of the original AlAs layer 3is changed into the AlO_(y) layer 13, the AlO_(y) layer can be formedstably and easily, with high mass-productivity. Still, since theremaining portion of the AlAs layer 3 that is not changed into theAlO_(y) layer is made coincident in configuration with the currentblocking layer 9, a larger amount of electric current flows through theperipheral region of the chip corresponding to the AlO_(y) layer 13.Therefore, a larger amount of light is generated at a peripheral portion6 a of the active layer 6. Since reflectance of the light-reflectinglayer is improved at peripheral regions of the chips, light 90 generatedat the peripheral portion 6 a of the active layer 6 is reflected at highefficiency so as to be extracted outside effectively without beinginterrupted by the electrode 12.

Further, since the light-reflecting layer is double structured of thefirst light-reflecting layer 3, 13 and the second light-reflecting layer4, even light 90A radiated from the active layer 6 toward the rear face(substrate) side so as to sneak to just under the electrode 12 can beeffectively reflected toward the top face side so as to be extractedoutside.

Actually, in this embodiment, chip luminous intensity at the emissionwavelength of 570 nm was able to be improved from normal 35 mcd to 60mcd. Further, the half-value width of the reflection spectrum increasedthreefold or more, compared with the half-value width of about 20 nm ofnormal light-reflecting layers. Thus, even with variations in layerthickness of the light-reflecting layer 4 in mass production,reflectance and reflection spectrum were less liable to variations, sothat the uniformity of luminous intensity was improved and the yield wasalso improved.

Although the foregoing embodiments have been described on a case of(Al_(x)Ga_(1-x))_(v)In_(1-v)P-based LEDs, the same effects can beproduced also with other LEDs, such as AlGaAs- or InGaAsP-based LEDs, orInGaAs- or GaInN-based LEDs. Further, the material to be changed intothe AlO_(y) layer is not limited to Al_(x)Ga_(1-x)As or the like, andthe same effects can be obtained also by such materials asAl_(x)Ga_(1-x)P, Al_(x)In_(1-x)P or Al_(x)In_(1-x)As.

Furthermore, although the foregoing embodiments have been described on asemiconductor light-emitting device including a GaAs substrate and an(Al_(x)Ga_(1-x))_(v)In_(1-v)P active layer, which are generally equal inlattice constant to each other, yet the present invention is applicablealso to those including other materials.

For instance, when sapphire is used for the substrate and the activelayer is formed by (Al_(w)Ga_(1-w))_(v)In_(1-v)N, it is appropriate touse (Al_(x)Ga_(1-x))_(v)In_(1-v)N for the conductive layer. It is alsopossible to use an(Al_(x)Ga_(1-x))_(v)In_(1-v)N/(Al_(z)Ga_(1-z))_(v)In_(1-v)Nsemiconductor multilayer film. In these cases, it is conditioned that0<w<z<x≦1, 0<v<1. The conditions for oxidizing the AlGaInN film may bechanged as required. As for the reason of this, although sapphire of thesubstrate and (Al_(w)Ga_(1-w))_(v)In_(1-v)N of the active layer areutterly different in lattice constant from each other, the crystal thinfilm formed on the substrate, given a normal chip size, exhibits thegenerally same properties as when it is in lattice matching with thesubstrate.

Furthermore, Si or GaN may also be used for the substrate. It isneedless to say that the same effects can be obtained also whenAl_(x)Ga_(1-x)As, (Al_(x)Ga_(1-x))_(v)In_(1-v)As,(Al_(x)Ga_(1-x))_(v)In_(1-v)Sb or the like is used for the active layer.

Sixth Embodiment

Integrating a high-intensity semiconductor light-emitting device asdescribed above with lenses allows an LED lamp of high luminousintensity to be obtained.

FIG. 14 shows an LED lamp 110 of a sixth embodiment using asemiconductor light-emitting device of the present invention.

This LED lamp 110 includes a semiconductor light-emitting device (chip)114 to which the present invention is applied, a first lead 113 on whichthe semiconductor light-emitting device 114 is mounted, and a secondlead 112 disposed so as to be spaced from the first lead 113. A rearface (n-side electrode 11) of the semiconductor light-emitting device114 is bonded to a leading end of the first lead 113 via electricallyconductive adhesive such as silver paste. A p-side electrode 12 of thesemiconductor light-emitting device 114 is connected to a leading end ofthe second lead 112 by a metal wire 116. Then, the semiconductorlight-emitting device 114 and portions of the first lead 113 and thesecond lead 112 near their leading ends are sealed by a transparentresin 115 composed of epoxy resin or the like. A fore end portion of thetransparent resin 115 is in the form of a hemispherical-shaped lens sothat light coming out from the semiconductor light-emitting device 114toward the top surface (p-side electrode 12) side is radiated forwardefficiently. Still, the semiconductor light-emitting device 114 exhibitshigher brightness than conventional semiconductor light-emittingdevices. Therefore, this LED lamp is enabled to show high luminousintensity.

As already described, since the semiconductor light-emitting device 114has a light-reflecting layer between active layer and substrate, thereoccurs less light reflected from the side faces of the chips.Accordingly, even if the leading end of the first lead 113, on which thesemiconductor light-emitting device 114 is mounted, is not formed into areflector-equipped configuration as in the figure, high luminousintensity can be achieved.

In addition, it is also possible to provide one lamp in one unit with aplurality of semiconductor light-emitting devices differing in activelayer material and therefore different in emission wavelength from eachother. That is, the second lead 112 is provided to a quantitycorresponding to the number of semiconductor light-emitting devices.Such a plurality of semiconductor light-emitting devices are disposed soas to be arrayed at the leading end of the common first lead 113. Thep-side electrodes 12 of the individual semiconductor light-emittingdevices are connected to their corresponding second leads 112 by Auwires, respectively. With such an arrangement, the plurality ofsemiconductor light-emitting devices having different emissionwavelengths can be applied with electric current independently from eachother. Accordingly, a high-intensity LED lamp which emit light in whiteand other various colors can be implemented.

Further, in order to achieve higher brightness, the lamp shown in FIG.14 may be grouped in a plurality to make up an integrated lamp. Such anintegrated lamp is suitable for traffic signals or the like to be usedoutdoors. In particular, the integrated lamp can be used for side lightsor buoys of ships that are required to have high visibility.

Furthermore, the above-described semiconductor light-emitting devicesmay be disposed integrally in a matrix to make up a display panel 120 asan LED display unit. With such an arrangement, a display panel showinghigh visibility even outdoors can be implemented. FIG. 15 shows anelectric circuit of such a display panel 120. In this case, referencecharacters LED 11, LED 12, . . . , LED 33 denote semiconductorlight-emitting devices to which the present invention is applied. To theLED 11, LED 12, . . . , LED 33 are connected protective diodes Z11, Z12,. . . , Z33 in parallel for the prevention of electrostatic breakage oftheir corresponding LEDs, respectively. It is noted that referencecharacters TR1, . . . , TR6 denote transistors for use of driving theLEDs.

In this example, each one LED and one protective diode are integrallyformed as one LED lamp. However, the LED is not limited to one innumber, and a plurality of LEDs may be integrated. In this case, theplurality of LEDs and protective diodes are connected all in parallel.Further, the plurality of LEDs may be those having the same emissionwavelength, in which case the brightness can be further enhanced.

This display panel 120 operates in the following way. For example, theLED 22, if desired, can be lit by turning on the transistor TR2, whichconnects to the LED 22 in the row direction, and the transistor TR5,which connects to the LED 22 in the column direction. In this case, ifthe protective diodes are one-way diodes, electric current flows along aroute Al as shown in the figure, so that the LEDs 11, 12, 21 may also bemis-lit. For this reason, the protective diodes are desirably providedby two-way ones, i.e., protective diodes that do not permit electriccurrent to pass therethrough unless the forward voltage becomes beyond aspecified value, irrespective of the direction of voltage.

The LED to be lit can be selected arbitrarily. The LED to be lit may beset as plural ones, without being limited to one.

It is clear by the above description that a semiconductor light-emittingdevice according to the present invention is capable of effectivelyextracting light emitted from the active layer to the external.

Furthermore, a semiconductor light-emitting device manufacturing methodaccording to the present invention is capable of fabricating suchsemiconductor light-emitting devices with high mass-productivity.

Still furthermore, an LED lamp and LED display according to the presentinvention can achieve higher brightness.

1. A method for manufacturing a semiconductor light-emitting device bystacking, on a semiconductor substrate, a plurality of layers includingan active layer made of a semiconductor which generates light of aspecified wavelength, the method comprising the steps of: providing,between the semiconductor substrate and the active layer, an Al richlayer higher in Al ratio than any other layer among the plurality oflayers; dividing into chips a wafer in which the plurality of layers arestacked, thereby making a side face of the Al rich layer exposed; andoxidizing Al contained in the Al rich layer from the exposed side face,thereby making a peripheral portion of the Al rich layer changed into anAlO_(y) layer.
 2. The method for manufacturing a semiconductorlight-emitting device according to claim 1, wherein the step ofoxidizing Al contained in the Al rich layer is carried out by leaving ina water vapor the chips in which the side face of the Al rich layer isexposed.
 3. The method for manufacturing a semiconductor light-emittingdevice according to claim 2, wherein the water vapor is introduced tothe side face of the Al rich layer by an inert gas that has been passedthrough boiling water.
 4. The method for manufacturing a semiconductorlight-emitting device according to claim 2, wherein the step ofoxidizing Al contained in the Al rich layer is carried out in anatmosphere having a temperature of 300° C. to 400° C.
 5. The method formanufacturing a semiconductor light-emitting device according to claim1, further comprising the step of: removing, by etching, the AlO_(y)layer formed at the peripheral portion of the Al rich layer.